1. Field of the Disclosure
The present invention relates to scintillating ceramic bodies, particularly, rare earth oxysulfide scintillating ceramic bodies that function to convert radiation such as X-ray radiation into visible light, and methods for forming such ceramic bodies.
2. Description of the Related Art
In fields such as the medical diagnostics and industrial non-destructive inspection, X-ray computed tomography (X-ray CT) has been widely used to characterize a patient or sample under inspection. In the context of X-ray CT, scintillators are employed to receive X-ray radiation and emit visible light in proportion to the incident radiation intensity.
Typically, scintillators are solid state, in the form of a single crystal such as NaI, CsI, and CdWO4. While single crystal scintillators have found widespread acceptance within the X-ray CT industry, the industry has continued to seek alternative polycrystalline scintillators. Polycrystalline ceramic scintillators represent a promising alternative to single crystal scintillators, with advantages such as lower processing costs and shorter processing times (higher throughput), superior material utilization through near-net shape processing, better homogeneity with respect to incorporation of dopants, and access to ceramic processing techniques that may allow for compositional flexibility to achieve novel scintillating compositions that cannot be prepared by growth from a melt/solution processing pathway.
In the context of polycrystalline ceramic scintillators, several different compositional families have been exploited. One family, rare earth oxides having the cubic crystal structure, has the generalized formula (Gd, Y)2O3: activator. Another class of materials, rare earth oxysulfides are particularly well-suited for highly sensitive radiation detectors including X-ray CT detectors. Rare earth oxysulfides may have the generalized formula (M1-xLnx)O2S, where M stands for at least one element from the group of rare earth elements and Ln represents an activator.
Rare earth oxysulfide ceramic scintillators have been produced by several processing pathways. In one, densification takes place through a ‘canning’ or encapsulation process. In this process, a gas-tight canned or encapsulated body is placed into a hot isostatic pressing (HIP) processing apparatus. Here, encapsulation in a can prior to HIPing is utilized particularly for components having open porosity, commonplace in the context of ceramic compositions that are difficult to densify. That is, ceramic bodies with open porosity generally cannot be properly densified utilizing gas HIPing (GHIPing), as direct application of pressurized gas (without presence of the gas-tight intermediate can) on a porous body generally results in gas penetration and only limited densification.
In a second, distinct processing pathway for forming rare earth oxysulfide scintillators, use has been made of sintering, including pressureless (atmospheric) sintering, low pressure sintering (e.g., 1-20 atm), and hot pressing (particularly with limited pressures). Such approaches have been used in connection with starting materials composed of morphologically controlled powders, such as powders having a high surface area that enables successful densification in low pressure processes, notably pressures lower than utilized in HIPing operations.
Despite successful formation of high density scintillators, the foregoing processing pathways are not without drawbacks. For example, the so-called canning approach is cumbersome and difficult to execute. The gas-tight container or can is difficult to fabricate, and recovery of the densified material within the container is difficult. The sintering approaches utilizing high surface area powders do not suffer from the same disadvantages, but nevertheless are expensive, and may have limited throughput such as in the context of hot pressing. In addition, the precise morphology, particle size distribution and powder surface area must be carefully controlled to ensure proper densification, increasing cost and adding process control challenges.
While not specifically in the context of ceramic scintillators, glass HIPing, in which a molten glass rather than a gas is used to transfer pressure to the material undergoing densification, has been utilized for hard-to-densify ceramic materials. However, glass HIPing has other processing challenges, such as tendency of the glass to penetrate porosity and inhibit proper densification, occurrence of unwanted interactions between the glass and the material, as well as difficulty in material removal following glass HIPing.
As should be clear, there is interest in the development of alternative processing methodologies, as well as novel scintillating bodies formed thereby.